As a model for understanding RNA-protein interactions, we are studying the structure of the Rev Response Element RNA in complex with peptides derived from the Rev protein. Rev is one of two small basic regulatory protein in HIV. Binding of Rev to the Rev-response element RNA results in a change in the ratio of spliceD and unspliced viral mRNAs that appear in the cytoplasm. Formation of this interaction is a key point in the replication cycle of HIV. In addition, we are also examining a model of the HIV TAR RNA in complex with argininamide and the base triple formed between an A-U base pair in the upper stem of HIV TAR RNA.